Clostridium difficile infection (CDI) is one of the most prolific causes of bacterial-induced diarrhea in the United States, with 3 million cases estimated annually. Newly emerged in its hypervirulent form, C. difficile also causes serious and potentially fatal inflammation of the colon. Because C. difficile is rapidly developing resistance to antibioti treatment, there is an urgent need to find an alternative therapy. Vancomycin and metronidazole remain treatment options for CDI, but neither is fully effective as is evident by the unacceptably high relapse rates. Two large enterotoxins (TcdA and TcdB) are the known causes of C. difficile-associated disease. Although an antitoxin vaccine program is currently in clinical trials, the efficacy of this approach remains highly uncertain since patients with severe CDI typically tend to be the elderly and the critically ill. Systemic antitoxin immunotherapy has recently been reported to be effective in preventing disease relapse in CDI patients, but fails to confer significant clinical benefits or reduce the length of hospitalization. Oral adaptation of passive antitoxin immunotherapy is currently not feasible or economical. Thus, there is an urgent need to develop new oral therapeutics for CDI. Our goal is to address these critical issues by performing highly innovative studies of the toxin virulence mechanism and by developing prototypic concepts for oral allosteric therapeutics that neutralize toxin activity in the colon. Tis work will be performed as a multi-institutional collaborative effort involving basic and clinical expertise of the C. difficile toxins, and in generating novel antitoxin therapeutics.